Field of the Invention
The present invention generally relates to methods and systems for subsea well intervention and work-over on seabed equipment, and more particularly to an Open Water Wireline (OWWL) or Spoolable Compliant Guide (SCG) well intervention system and method, including a control umbilical (CU), preferably a multipurpose control umbilical (MCU), deployed and managed using a dedicated remotely operated or autonomous umbilical management system unit (UMSU), wherein the CU or MCU is connected via the UMSU to one or more tethers that connect in turn to one or more subsea equipment.
Background
Well intervention and work-over on seabed equipment, such as subsea oil wells, can be performed using open water wireline (OWWL) or Spoolable Compliant Guide (SCG) systems. During these work-over operations, the main functions of the seabed equipment are typically, if not always, required to be remotely controlled and operated from a support ship or rig, which is in attendance. Such control includes the communication or transfer of one or more types of media, including data, electrical power, hydraulic power and a chemical treatment fluid or fluids. In order to provide such control, the media is communicated through one or more umbilicals which are launched from the support ship or rig for the purpose of connecting the support ship or rig to the seabed equipment.
However, there exist a number of problems that must be solved before such well intervention systems can become widely accepted in the industry. Existing intervention and work-over methods and systems suffer from various discovered problems, as further described herein. There are certain characteristics of the Open Water Wireline (OWWL) or Spoolable Compliant Guide (SCG) methods and systems that complicate the design of the control umbilicals and can in certain cases create problems that affect the smooth running of the subsea work-over operation. For example, due to the up and down heaving motion of the support vessel or rig caused by the ocean waves, a control umbilical is generally required to be somehow tensioned in order to prevent it from buckling or crumpling under the resulting compressive forces and displacements that can arise. The construction of a typical control umbilical is such that exposure to compressive forces and displacements is generally undesirable during operation.
Another problem of free hanging umbilicals arises when environmental conditions, such as a subsea current, and the like, cause the umbilical to deflect without control in the water column. One known area of concern of such behavior is the twisting or looping of the umbilical on itself. During recovery of the umbilical, this loop can close itself and as such permanently damage the umbilical. Another concern with the horizontal excursion is the potential contact between the umbilical system and other downlines, with the potential risk of damage to the umbilical. This problem can occur when additional lines are placed in the water column that could cause clashing or tangling of the lines. In this case, it is extremely important to actively manage one or more of such cables to keep them from clashing.
The above issues may be reduced somewhat with the use of a plurality and smaller umbilicals. For example, a smaller umbilical may be used incorporating only the electrical power and communication cables or fibers similar to those commonly used by Remotely Operated Vehicles (ROVs). U.S. Patent Application Publication No. 20060231264 assigned to SAIPEM describes an open light well intervention system that employs as a data communication and power supply umbilical the umbilical of the ROV. However, this solution is limited. One problem of the SAIPEM system is that it would require multiple umbilicals to supply the functions needed by the different subsea equipment identified, and which consist of both the intervention equipment and the ROV. Also, such an arrangement has practical limitations in that the deployment of both the intervention equipment and the ROV are dependent on each other.
One known method for keeping an umbilical under a constant tension employs a constant tension winch positioned on the vessel. Such systems have a disadvantage that, in tensioning the umbilical, they cause the umbilical to be repeatedly bent and straightened out again at a number of locations, e.g., on sheaves or in bends and that over time cause fatigue and/or internal friction damage, eventually leading to failure of internal cables or tubes contained in the umbilical.
Constant tension winch systems also have the disadvantage that they are generally expensive in terms of procurement of the specialized winch required. Also, constant tension winch techniques would be generally very difficult to implement in deepwater because the weight of the umbilical will by necessity increase to account for the increasing water depth. Thus, the lengthy heavy umbilical itself and the constant tension winch will need to become very large and hence there will be a correspondingly undesirable economic impact to the work-over activity.
In addition, existing tensioned umbilical methods generally require the vessel to be operated at or close to the vertical center of the seabed equipment it controls and, typically, require the umbilical to be connected to the seabed equipment on surface before being run with the seabed equipment, while the latter is deployed. U.S. Pat. No. 6,223,675 describes an underwater apparatus for performing subsurface operations. The apparatus includes a linelatch system that is made up of a tether management system (TMS) connected to a flying latch vehicle by a tether. The TMS controls the amount of free tether between itself and the flying latch vehicle using a reeling in and out system well known in the art. The TMS is lowered and positioned to the seafloor using an umbilical, which is then disconnected from the tether management system. The TMS is connected to the underwater subsea equipment via the flying latch vehicle.
However, none of the above systems provide a fully satisfactory umbilical solution for underwater intervention systems. Most existing systems cannot be deployed and connected to the intervention seabed package readily and are subject excessive bending and stressing of the umbilical that causes over time fatigue, damage and failure of internal cables and tubes contained in the umbilical.